(a) Technical Field
The present invention relates to a polypropylene resin composition for automobile interior trim parts with superior paint adhesivity and low specific gravity.
(b) Background Art
Materials for automobile interior parts, such as instrument panels and door trim panels, should have superior paint adhesivity and impact resistance in order to satisfy vehicle collision standards. A mixture of polycarbonate and acrylonitrile-butadiene-styrene copolymer, which has a polar structure that provides superior paint adhesivity and impact resistance, is widely used. However, the resin is very expensive and has a high specific gravity. Thus, a lot of efforts in the automobile industry are focused on developing an alternative material with low specific gravity.
As one alternative, a polyolefin-based thermoplastic resin, particularly a polypropylene-based resin, is frequently used. However, since the polypropylene-based resin consists of semicrystalline polypropylene and lacks polar or reactive groups, it cannot form a strong polar bond or hydrogen bond with polar molecules included in paints. Therefore, it demonstrates poor impact resistance and paint adhesivity.
Recently, ethylene-α-copolymer rubber has been blended with the polypropylene-based resin to improve impact resistance. Further, primer treatment is performed before painting to improve the adherence of the paint to the surface.
In particular, the primer treatment is carried out to modify the surface before painting the polypropylene-based resin. For example, coating of a chlorinated polypropylene (CPP) primer, flame treatment, corona treatment, plasma treatment, ion or electron beam treatment, etc. are employed after injection molding of the parts. Among these methods, CPP primer treatment is the most widely used because it provides superior paint adhesivity and productivity. However, the surface treatment by CPP primer treatment before painting has problems associated with increased cost, environmental concern of the chlorine components contained in the CPP primer, removal of the primer for recycling, and the like.
Accordingly, efforts have been made to develop a low-specific-gravity polypropylene-based resin that can be used for automobile interior parts, which has superior physical properties and exhibits superior paint adhesivity without primer treatment.
Many methods for improving physical properties and paint adhesivity of polypropylene have been proposed. A representative example is addition of an olefin copolymer rubber, an olefin-based oligomer having hydroxyl groups, an olefin-acrylate copolymer, a glycidyl methacrylate copolymer, etc. to polypropylene resin in order to polarize the resin and improve its reactivity and adhesivity with paints.
As for automobiles interior materials using polypropylene, Korean Patent No. 957303 describes a polypropylene resin composition including an ethylene-propylene block copolymer, an ethylene-α-olefin copolymer rubber, a styrene-based polymer rubber, a polypropylene-silicone rubber masterbatch, a magnesium compound and an inorganic filler.
U.S. Pat. No. 7,375,162 describes a propylene polymer composition including a propylene-ethylene copolymer base resin, an inorganic filler such as magnesium hydroxide and an ethylene-butene-1 copolymer plastomer.
Japanese Patent Publication No. 2011-0088997 describes a composite material including an olefin-based rubber such as block polypropylene, ethylene-butene copolymer, etc. and an alkaline compound such as magnesium hydroxide.
However, the above-described technologies are problematic in that reproducibility is not good, paint adhesivity is insufficient and impact resistance is not satisfactory to meet the strict vehicle collision standards.
Accordingly, development of a polypropylene-based resin composition having improved impact resistance and paint adhesivity is needed.